Portable apparatus using flash memory are more and more popular among general consumers. Various types of flash memory cards for use with these apparatus are also quickly developed and introduced into the market. Among others, CompactFlash Type I & II (CF), Microdrive (MD), SmartMedia (SM), Memory Stick (MS), MS Pro, MS Duo, MultiMedia Card (MMC), Secure Digital (SD), and the recent xD Picture Card (xD) are the currently most popular types of flash memory cards.
Before the flash memory card reader has been developed, most apparatus, such as digital cameras, are directly connected to a computer via a serial port or a universal serial bus (USB) line. This type of connection is all right for small files. However, with the introduction of more complete apparatus and high-capacity flash memory cards, the size of data files increases in multiplication. Although there are still apparatus directly connected to the computer via the serial port or the USB line, these apparatus have been improved to enable convenient ejection of a flash memory card therefrom for inserting in a flash memory card reader. Moreover, to match various currently available flash memory cards, dual-slot or even multi-slot card readers have been developed. It is apparent the card reader is an electronic product getting more and more popular among consumers.
However, all electronic products have the problem of overcurrent (that is, short circuit). When a short-circuited and damaged flash memory card is inserted in a slot on the card reader, or there is defect in the produced card reader, or a user carelessly admits electrically conductive material, such as water or coin, into the card slot to result in short circuit of the card reader, not only the card reader and the flash memory card, but also the connected computer would be seriously damaged. Nevertheless, most card readers currently available in the market are not provided with means for complete overcurrent protection.
FIG. 3 is a block diagram showing the connection of a conventional memory card reader 3 with a USB interface 4; FIG. 4 is a schematic diagram showing a short-circuit-detecting protection circuit 6 for the conventional memory card reader 3; and FIG. 5 is a schematic perspective view of the conventional memory card reader 3.
As shown, the conventional memory card reader 3 is internally provided with a single chip 31, which is electrically connected to the USB interface 4. With the USB standard interface, the memory card reader has the ability of hot attach & detach. The single chip 31 is also electrically connected to a card reading unit 32, which reads/writes data from/into a memory card 5 inserted in a card slot 30 on the card reader 3.
More specifically, to enable the use of single chip and USB standard interface, the conventional memory card reader 3 achieves the ability of hot attach & detach by including a USB interface unit 4 that is electrically connected to a single chip 31 to perform data transmission and thereby provides data to the memory card reader 3.
When a user inserts a memory card 5 in a card slot 30 on the card reader 3, data are read from or written into the memory card 5 via a card reading unit 32.
The single chip 31 is electrically connected to the USB interface unit 4, so that the memory card reader 3 achieves the ability of hot attach & detach via the USB standard interface. Since the single chip 31 has bi-directional input/output function, sequential transmission and detection of the memory card 5 is not a problem. Moreover, in practical applications, the same function may be equally achieved using software instead of hardware, such as a finite-state machine (FSM). When a clock circuit is integrated into the single chip 31, it is not necessary to buy an additional IC at extra expense.
The conventional memory card reader 3 is provided with a software detection and protection circuit 6 that includes an external transistor 33 for controlling power supply to the card, and uses software to detect any voltage drop in the memory card 5. When a short circuit in the memory card 5 results in a voltage drop, the single chip 31 would turn off the transistor 33. Meanwhile, for the purpose of preventing impact by high amount of instantaneous current, a resistance capacitance delay unit 34 is interposed at an intermediate feedback path to moderate voltage rise and voltage drop.
In the case of a conventional one-slot card reader, it is automatically powered off when an overcurrent (that is, a short circuit) occurs at the card slot. That is, the whole card reader is off. In the case of a conventional multi-slot card reader, the whole card reader is automatically powered off when any one of the multiple slots is overcurrent (short-circuited). At this point, other normal card slots on the card reader are disabled at the same time. The user could not clearly know the exact card slot that is overcurrent, forming confusions in using the card reader.
It is therefore tried by the inventor to develop a method of overcurrent protection for multi-slot flash memory card reader, so that the card reader or other apparatus connected thereto is protected against damage when an overcurrent occurs, and a user is enabled to clearly know the exact point on the card reader where the overcurrent occurs.